1. Homeostasis

2. Objectives Discuss the importance of homeostasis
Explore how negative feedback systems work
Work through specific feedback systems used to maintain blood glucose and body temperature

3. It Is All About Balance…
All living things must react to their environment to survive
Homeostasis regulated stable state; constantly adjusting
Unicellular direct contact with world
Multicellular ???
Most internal cells do not have direct contact
ECF (extracellular fluid)
Plasma
Tissue fluid

4. Types of Adjustment What are the two ways an organism can change?
Regulators adjust to resist environment and maintain a stable state
Warm-blooded animals (thermo regulators)
Conformers adjust to match environment to maintain their stable state
Cold-blooded animals (thermo conformers)
Either method, what things must be regulated in all living things?
Concentration of nutrients, O2, CO2, waste, water, NaCl, pH, and plasma
Temperature

5. Types of Homeostasis
Complex organisms require multiple levels of homeostasis to stay alive
Cells maintain this own homeostasis but must work together in a complex organism
Local homeostatic controls organs/tissue adjusting to demands
Stomach maintains pH low enough to work but not low enough to hurt stomach
Systemic homeostatic controls organs regulate other organs
Hypothalamus (part of brain)

6. Feedback Systems: Key to Homeostasis
Negative feedback keep homeostasis regulated most of the time
Stimulus environmental change
Receptor senses stimulus (input)
Integrator compares information from sensor to set point (normal level)
Effector response from integrator (output)
Example: It is cold in this room
Stimulus cold
Receptor temp. sensor in heater (18oC)
Integrator computer compares temp. sensor to set point temp. (25oC)
Effector heater turn on until room is 25oC

7. Homeostasis In Living Things
We are not perfect machines; homeostasis always fluctuates around a set point
What is the average pulse rate of the human heart?
60 Beats/min
60 beats is our set point; but you rarely get 60 beats/min
Fluctuate above and below 60; average out to set point

8. Feedback Loops: Blood Glucose
Glucose is major source of energy (respiration)
Regulated by two hormones and negative feedback inhibition
Glucagon promotes breakdown of glycogen to release glucose; happens when hungry or during exercise
Insulin lowers glucose levels in blood after eating by
Diabetes cannot regulate glucose because defective or missing insulin

9. Regulating Blood Glucose
You study all morning; running low on energy
Blood glucose is too low!!
Hypothalamus tells pancreas to release glucagon; glycogen glucose
Blood glucose back to normal
LUNCH TIME!! You eat and digestion breaks starch into glucose
Blood glucose too high!!
Hypothalamus tells pancreas to release insulin; liver, muscles, fat tissue absorb glucose
Repeat all day!

10. Layers of the Skin What is the job of the skin? Hair/Fur:
Protect the body
Stop pathogens from entering
Prevent water loss
Detect changes in temp. and pressure
Detect pain
Regulate heat loss
Hair/Fur:
Cold weather hair stand up to help trap air around skin
Hot weather hair lays flat to limit air around ski
Fat layer insulates body against cold

11. Feedback Loop: Body Temp
What is the homeostatic point for body temp?
37oC
In hot weather:
Skin sends info to hypothalamus
Vasodilation arteries expand to release heat by radiation
Sweat glands salty sweat evaporates from skin which cools you down

12. Feedback Loop: Body Temp (part 2)
In cold weather:
Skin sends info to hypythalamus
Vasoconstriction arterioles shrink to keep
Sweat glands stop producing sweat
Shivering muscle contractions burn ATP to generate more heat